[C++11] Turn off compiler-based detection of R-value references, relying
on the fact that we now build in C++11 mode with modern compilers. This
should flush out any issues. If the build bots are happy with this, I'll
GC all the code for coping without R-value references.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202574 91177308-0d34-0410-b5e6-96231b3b80d8